I. Malnar et al., HAMMETT RHO(+) VALUES AS KINETIC EVIDENCE FOR THE CONCERTED BIOMIMETIC BICYCLIZATION MECHANISM, Journal of organic chemistry, 63(9), 1998, pp. 3041-3044
Chlorides 1 (1-aryl-1-chloro-5,9-dimethyl-5,9-undecadienes) with vario
us phenyl substituents were prepared (Y = p-OCH3, p-CH3, H, p-Br, and
m-Br), and solvolysis rates were measured in 80% (v/v) aqueous ethanol
and in 97% (wt/wt) aqueous 2,2,2-trifluoroethanol. The Hammett rho(+)
values obtained are -1.5 and -1.8, respectively, indicating the conce
rted bicyclization. Comparison with rho(+) values that correspond to s
olvolysis of the benzylic squalene derivatives 3 (rho(+) = -1.8 and -1
.6 in the same solvents) leads to the conclusion of the concerted bicy
clization in 3 and may also suggest concerted bicyclization under biom
imetic conditions in the natural precursor, 2,3-epoxysqualene, as well
.